In JP-B-6-86222 (hereinbelow “Patent Document 1”), a vehicle steering apparatus is disclosed which is constructed to control an angle of travel direction of a motor vehicle in accordance with a steering angle of a steering operator member, such as a steering wheel, of the vehicle, i.e. an angle of travel direction designated by a human operator or driver via the steering operator member. Further, in JP-A-6-92250 (herein-below “Patent Document 2”), a vehicle steering apparatus is disclosed which is constructed to control a travel direction of a motor vehicle in response to vehicle driver's operation of a steering wheel with increased stability and increased followability with respect to the steering wheel operation.
Specifically, the steering apparatus disclosed in Patent Document 1, provided with a power steering mechanism for changing an orientation or steering angle of steerable road wheels of the motor vehicle via an actuator, includes a direction designation section for, in response to operation by the human operator or driver, designating an angle of travel direction of the vehicle relative to a predetermined reference absolute azimuth, and a travel direction detection section for detecting an actual angle of travel direction of the vehicle relative to the predetermined reference absolute azimuth. The disclosed steering apparatus also includes a control section for controlling the power steering mechanism so as to eliminate a deviation or offset between the designated angle travel direction and the detected actual angle of travel direction on the basis of output signals from the steering direction designation section and travel direction detection section.
The steering apparatus disclosed in Patent Document 2 includes a steering direction designation section for designating a travel-direction variation amount of the motor vehicle relative to a predetermined reference direction, a travel direction detection section for detecting an actual travel-direction variation amount of the vehicle, and a control section for controlling a power steering mechanism so as to eliminate an offset between the designated travel-direction variation amount and the detected actual travel-direction variation amount (i.e., angle-of-travel-direction offset). Here, the control section includes a road-wheel-steering-angle designation section for outputting a signal indicative of a target road-wheel steering angle on the basis of the angle-of-travel-direction offset, and the road-wheel-steering-angle designation section is constructed to reduce the road-wheel steering angle as a traveling velocity of the motor vehicle increases.
According to each of the prior art techniques disclosed in Patent Document 1 and Patent Document 2, the steering mechanism is controlled so as to eliminate the offset between the angle of travel direction designated by the driver and the detected actual angle of travel direction relative to the predetermined reference azimuth.
FIG. 11 is a block diagram showing a general hardware setup of a control device in traditional vehicle steering apparatus. The control device 100 includes an offset calculation section 101, an angle-of-travel-direction input section (i.e., steering operator member) 102 operable by the vehicle driver to designate an angle of travel direction of the motor vehicle, a designated angle detection section 103, and an electronic control unit (ECU) 104. The control device 100 also includes a steering angle generation section (e.g., steeling motor) 105, a yaw rate detection section 107, an integrator 108, a front-gazing-point detection section 109, a vehicle velocity detection section 110, another integrator 111, and an adder 112. The electronic control unit 104 includes a road-wheel steering angle gain section 113, and a steering motor drive section 114.
The offset calculation section 101 calculates a deviation or offset between a target travel course set by the vehicle driver and a value obtained by adding a front point gazed by the vehicle driver facing straight ahead (“front gazing point”) detected by the front-gazing-point detection section 109 and a current position of the vehicle, and outputs a calculated offset, so that the driver can determine, on the basis of the thus-calculated offset in the travel course of the motor vehicle 106, how great the angle of travel direction to be input or designated should be.
The angle-of-travel-direction input section 102 comprises a steering operator member, such as the steering wheel, of the motor vehicle 106, which is operable by the driver to input a target angle of travel direction on the basis of the offset output from the offset calculation section 101. In the case where the steering operator member 102 is the steering wheel, an angle through which the driver has turned the steering wheel (i.e., steering angle of the steering wheel) is input or designated as the target angle of travel direction. The designated angle detection section 103 detects the target angle of travel direction input or designated by the driver through the steering operator member 102 and thereby outputs a driver-designated steering angle θ (i.e., steering angle of the steering operator member, such as the steering wheel) to the road-wheel steering angle gain section 113 of the electronic control unit 104.
On the basis of the driver-designated steering angle θ input via the designated angle detection section 103, the electronic control unit 104 outputs a drive signal to drive the road-wheel steering angle generation section (i.e. steering motor) 105.
The steering motor 105 includes a gear mechanism etc. In a case where the steering motor 105 comprises a DC motor and the steering angle of the motor vehicle 106 is controlled on the basis of a polarity and intensity value of a motor current to be supplied to the DC motor 105, the steering motor drive section 114 supplies the steering motor 105 with a predetermined motor current of a predetermined polarity corresponding to a target road-wheel steering angle δ. Where the steering motor 105 comprises a pulse motor, the steering motor drive section 114 is constructed to supply a necessary number of pulses for forward or reverse rotation of the pulse motor 105.
Travel direction of the motor vehicle 106 is varied in accordance with the target road-wheel steering angle δ generated by the steering motor 105, and resultant variation of the travel direction of the vehicle produces a yaw rate Υ in the motor vehicle 106. The thus-produced yaw rate Υ is detected by the yaw rate detection section 107. The integrator 108 integrates the yaw rate Υ to thereby output a current angle of travel direction Ψ of the motor vehicle 106. The front-gazing-point detection section 109 detects a front point gazed by the vehicle driver that is generally determined by the angle of travel direction Ψ output from the integrator 108, and it outputs a value pertaining to a position of the front gazing point to the adder 112. The vehicle velocity detection section 110 detects a traveling velocity of the motor vehicle 106 and outputs the detected velocity to the integrator 111. The integrator 111 integrates the vehicle velocity V to thereby output a value pertaining to a current position of the vehicle 106. The adder 112 adds together the values pertaining to the position of the front gazing point and position of the motor vehicle 106, to thereby output information representative of a current travel course of the vehicle 106.
Then, the vehicle driver inputs a target angle of travel direction of the motor vehicle 106 by predicting, on the basis of the outputs of the control device 100, a deviation between a target travel course and an actual travel course of the vehicle 106. In response to the input target angle of travel direction, the control device 100 activates the steering motor 105 to impart a target road-wheel steering angle to steerable wheels of the vehicle 106 over an electric wire, so that the travel direction of the vehicle 106 is varied and thus a yaw rate corresponding to the travel direction variation is produced. Then, the angle of travel direction of the vehicle 106 is controlled in accordance with a value obtained by the integrator 108 integrating the travel direction variation.
The road-wheel steering angle gain section (i.e., road-wheel steering angle calculation section) 113 generates a signal indicative of a target road-wheel steering angle δ, on the basis of a signal indicative of the driver-input or driver-designated designated steering angle θ. This road-wheel steering angle calculation section 113 includes a conversion table, for example in the form of a ROM, prestoring various road-wheel steering angles preset in association with various possible driver-designated steering angles θ of the steering operator member. Alternatively, the road-wheel steering angle gain section 113 may be arranged to calculate a target road-wheel steering angle δ on the basis of a pre-registered function expression or in any other suitable manner.
On the basis of the target road-wheel steering angle signal output from the angle calculation section 113, the steering motor drive section 114 generates a drive signal for driving the steering motor 105.
FIG. 12 is a block diagram showing a general hardware setup of the control device in the vehicle steering apparatus disclosed in Patent Document 1 and Patent Document 2. The control device 200 includes an offset calculation section 201, an angle-of-travel-direction input section (i.e., steering operator member) 202, a designated angle detection section 203, a resistive force generating motor (or steering resistive force generating actuator) 204, and an electronic control unit (ECU) 205. The control device 200 also includes a road-wheel steering angle generation section(steering motor) 206, a yaw rate detection section 207a, an integrator 208, a travel direction detection section 209, a front-gazing-point detection section 210, a vehicle velocity detection section 211, and another integrator 212. The electronic control unit 205 includes a driver-designated angle corresponding section (designated angle gain section) 214, an offset calculation section 215, and a road-wheel steering angle calculation section including a road-wheel steering angle designation section 216 and road-wheel steering angle control section 217. The electronic control unit 205 also includes a steering motor drive section 218, an angle-of-travel-direction calculation section including an angle gain section 220 and angle calculation section 219, a steering resistive force calculation section (or steering resistive force setting section) 221, and a resistive motor drive section (or steering resistive force actuator drive section) 222. The motor vehicle 207 includes steerable road wheels, a vehicle velocity detection section 211, etc.
In the control device 200, the offset calculation section 201 calculates an offset between a target travel course set by the vehicle driver and a value obtained by adding a front point gazed by the driver (i.e., “front gazing point”) facing straight ahead detected by the front-gazing-point detection section 109 and a current position of the vehicle, and outputs a calculated offset, so that the driver can determine, on the basis of the thus-calculated offset in the travel course of the motor vehicle, how great the angle of travel direction to be input or designated should be.
The angle-of-travel-direction input section 202 comprises a steering operator member, such as the steering wheel, of the vehicle, which is operable by the vehicle driver to input a target angle of travel direction. In the case where the steering operator member 202 is the steering wheel, an angle through which the driver has turned the steering wheel is input or designated as the target angle of travel direction. The designated angle detection section 203 detects the target angle of travel direction input or designated by the driver through the steering operator member 202 and thereby outputs a driver-designated steering angle θ (i.e., steering angle of the steering operator member) to the driver-designated angle corresponding section (designated angle gain section) 214 of the electronic control unit 205. The resistive force generating motor 204 is controlled by the electronic control unit 205 to give a steering resistive force to the steering operator member 202.
The electronic control unit 205 generates a drive signal for driving the steering motor on the basis of the driver-designated steering angle θ detected via the detection section 203, vehicle velocity detected by the vehicle velocity detection section 211 and travel direction (yaw angle) detected by the travel direction detection section 209, and it drives the steering motor 206 in accordance with the drive signal. Also, on the basis of the driver-designated steering angle θ and vehicle velocity, the electronic control unit 205 generates a drive signal for driving the resistive force generating motor 204.
In response to the target angle of travel direction input by the vehicle driver via the steering operator member 202, the control device 200 activates the steering motor 206 to impart a target road-wheel steering angle to the steerable wheels of the vehicle 207, so that the travel direction of the vehicle 207 is varied and thus a yaw rate corresponding to the travel direction variation is produced. Then, the angle of travel direction of the vehicle 207 is controlled in accordance with a value obtained by the integrator 208 integrating the travel direction variation.
The driver-designated angle corresponding section 214 of the electronic control unit 205 generates a signal indicative of a target value K·θ of the angle of travel direction on the basis of a signal indicative of the angle of travel direction θ detected by the detection section 203. Ratio K between the angle of travel direction θ and target value K·θ of the angle of travel direction may be set to a desired value.
If the ratio K is set to “1.0”, the angle of travel direction θ and target value K·θ of the angle of travel direction equal each other; namely, when the steering operator member 202 has been turned rightward or clockwise through 180 degrees while the motor vehicle 207 is traveling northwards, the target value K·θ is changed to a value representative of a “southward” travel direction. If the ratio K is set to “0.5”, and when the steering operator member 202 has been turned clockwise through 180 degrees while the vehicle 207 is traveling northward, the target value K·θ is changed to a value representative of a travel direction 90 degrees clockwise from the current travel direction (e.g., eastward travel direction).
The angle-of-travel-direction calculation section, including the angle calculation section 219 and angle gain section 220, includes a means for integrating a signal indicative of the yaw rate Υ detected by the travel direction detection section 209, which generates a signal indicative of a current travel direction Kn·Ψ of the motor vehicle obtained on the basis of the yaw rate signal.
The offset calculation section 215 calculates an offset E between the signal indicative of the target value K·θ of the angle of travel direction output from the driver-designated angle corresponding section 214 and the signal indicative of the current travel direction Kn·Ψ output from the angle-of-travel-direction calculation section (angle calculation section 219 and angle gain section 220), to thereby supply a signal indicative of the calculated offset E (E=K·θ−Kn·Ψ) to the road-wheel steering angle calculation section (road-wheel steering angle designation section 216 and road-wheel steering angle control section 217).
The road-wheel steering angle calculation section (road-wheel steering angle designation section 216 and road-wheel steering angle control section 217) generates a signal indicative of a target road-wheel steering angle δ, on the basis of the signal indicative of the calculated offset E and the signal indicative of the detected vehicle velocity V This road-wheel steering angle calculation section includes a conversion table, for example in the form of a ROM, prestoring various target road-wheel steering angles δ preset in association with various possible offsets E and vehicle velocities V. Alternatively, the road-wheel steering angle calculation section may be arranged to calculate a target road-wheel steering angle δ on the basis of a pre-registered function expression or in any other suitable manner.
On the basis of the target road-wheel steering angle signal output from the road-wheel steering angle calculation section (road-wheel steering angle control section 217), the steering motor drive section 218 generates a drive signal for driving the steering motor 206. The steering motor 206 includes a gear mechanism etc. In a case where the steering motor 206 comprises a DC motor and the steering angle of the motor vehicle is controlled on the basis of a polarity and intensity value of a motor current to be supplied to the DC motor 206, the steering motor drive section 218 supplies the motor 206 with a predetermined motor current of a predetermined polarity corresponding to a target steering value δ. Where the steering motor 206 comprises a pulse motor, the steering motor drive section 218 is constructed to supply a necessary number of pulses for forward or reverse rotation of the pulse motor 206.
The steering resistive force calculation section (or steering resistive force setting section) 221 generates a signal indicative of a target resistive torque value T, on the basis of the angle offset E and vehicle velocity V. For this purpose, the steering resistive force calculation section 221 includes a conversion table, for example in the form of a ROM, prestoring various target resistive torque values T preset in association with various possible angle offsets E and vehicle velocities V. Alternatively, the steering resistive force calculation section 221 may be arranged to calculate a target resistive torque value T on the basis of a pre-registered function expression or in any other suitable manner.
The resistive motor drive section (or steering resistive force actuator drive section) 222 generates a drive signal for driving the resistive force generating motor 204.
The motor vehicle 207, integrator 208, front-gazing-point detection section 210, vehicle velocity detection section 211, integrator 212 and adder 213 shown in FIG. 12 are similar in construction and function to the motor vehicle 106, integrator 108, front-gazing-point detection section 109, vehicle velocity detection section 110, integrator 111 and adder 112 shown in FIG. 11.
In the conventional vehicle steering systems, the target road-wheel steering angle is set to be proportional to the steering angle of the steering operator member (i.e., driver-designated steering angle). However, because the steering angle of the steering operator member indicates an ultimate target control value in the techniques disclosed in Patent Document 1 and Patent Document 2, there has been a demand for a means which allows the vehicle driver to directly control the behavior of the vehicle by designating a desired angle of travel direction via the steering operator member, such as a means for controlling the vehicle with an enhanced accuracy in response to driver-designated angle of travel direction and in accordance with a changing road shape.